An electrophotographic photosensitive member (organic electrophotographic photosensitive member) including an undercoat layer containing metal oxide particles and a photosensitive layer formed on the undercoat layer and containing a charge-generating substance and a charge-transporting substance is used in electrophotographic apparatuses.
For example, titanium oxide particles, tin oxide particles, and zinc oxide particles are used as the metal oxide particles. In particular, it is known that the resistance of zinc oxide particles easily changes depending on the degree of oxygen deficiency and that the larger the oxygen deficiency, the lower the resistance of the zinc oxide particles.
These metal oxide particles are subjected to a surface treatment with a silane coupling agent in order to suppress the generation of black spot-like image defects caused by charge injection from a support to the photosensitive layer side. However, when the undercoat layer contains such surface-treated metal oxide particles, the resistance of the undercoat layer is increased and a variation in the electric potential (such as a variation in the light-area potential) in repeated use tends to be significant.
As for a technology for suppressing a variation in the light-area potential, PTL 1 discloses a technology in which zinc oxide particles provided with an acceptor compound (organic compound) are incorporated in an undercoat layer of an electrophotographic photosensitive member. PTL 2 discloses a technology in which a plurality of undercoat layers each contain a silane coupling agent, and one of the undercoat layers disposed on the photosensitive layer side has a higher concentration of the silane coupling agent.